Chemical Reactions and Chemical Reactions and EvidenceEvidence

A) Chemical ReactionsA) Chemical Reactions Chemical Reaction- Chemical Reaction- the process that turns one set of the process that turns one set of

chemical substances into another one setchemical substances into another one set Chemical reactions are studied by specialized scientist Chemical reactions are studied by specialized scientist

called called chemist-chemist-they study all things atomicthey study all things atomicAntoine-Laurent de LavoisierAntoine-Laurent de Lavoisier is considered to be the is considered to be the

father of modern chemistry, thanks to his intensive study father of modern chemistry, thanks to his intensive study of reactions during the mid 1700’sof reactions during the mid 1700’s Was the first to publish the law of conservation of massWas the first to publish the law of conservation of mass The total mass of things that go into a reaction(products) The total mass of things that go into a reaction(products)

equals the total mass of all things that are produced during equals the total mass of all things that are produced during the reaction(products)the reaction(products)

Mass is neither created or destroyed in a RXN, it only Mass is neither created or destroyed in a RXN, it only changes formschanges forms

How do we know when a chemical reaction has taken place?

Absorb or Release of Heat -gets hot or gets cold or releases light ?

Production of a Gas -can you smell it, like something rotting? -do you see bubbles in the liquid?

Formation of a solid, called a precipitate -it “rains” or precipitates out of the solution-it is usually a different color?

Chemical Vs. Physical ChangeChemical Vs. Physical Change

Physical changes are only concerned with Physical changes are only concerned with changes in energy or states of matter changes in energy or states of matter ( S,L,G)( S,L,G)

Starting and ending material are the same Starting and ending material are the same thing, thought they may look differentthing, thought they may look different EX- Ice melting, Water evaporatingEX- Ice melting, Water evaporating

B) Writing Chemical ReactionsWhen a clear aqueous solution of potassium iodide is mixed with a clear aqueous solution of lead nitrate it produces(yields ) a clear solution of potassium nitrate and a yellow solid precipitate called lead(II) iodide

Pb(NO3)2 (aq) + KI(aq) PbI2 (s) + KNO3(aq)

Reactants Products

Symbols Used in an EquationSymbols Used in an Equation

(g) means gaseous phase(g) means gaseous phase (l) means liquid phase(l) means liquid phase (s) means solid phase(s) means solid phase (aq) means dissolved in water(aq) means dissolved in water means yield (produces)means yield (produces)

Writing Word EquationsWriting Word Equations

Aqueous silver nitrate reacts with solid Aqueous silver nitrate reacts with solid copper metal to form solid silver and copper metal to form solid silver and copper (II) nitrate.copper (II) nitrate.

Types of Chemical ReactionsTypes of Chemical Reactions Synthesis or CombinationSynthesis or Combination

Two or more substances chemically combine to Two or more substances chemically combine to become one substancebecome one substance

PatternPatternA + BA + B ABAB

+ +

Mg + ClMg + Cl22 MgClMgCl22

__

Types of Rxns. Cont…Types of Rxns. Cont…

DecompositionDecomposition One substance breaks down into two or more One substance breaks down into two or more

substances.substances. PatternPattern

• AB AB A + BA + B

++

MgClMgCl22 Mg + ClMg + Cl22

Types of Rxns. Cont.Types of Rxns. Cont.

Single ReplacementSingle Replacement When a single element switches placement When a single element switches placement

with the anion or cation of another compoundwith the anion or cation of another compound PatternPattern

• AB + C AC + BAB + C AC + B

• + + + +

NaCl + K Na + KClNaCl + K Na + KCl

Types of Rxns. Cont.Types of Rxns. Cont.

Double ReplacementDouble Replacement When the cations and anions of two different When the cations and anions of two different

compounds switch placescompounds switch places PatternPattern

• AB + CD AD + CBAB + CD AD + CB

• + + + +

KCl + MgOH KOH + MgClKCl + MgOH KOH + MgCl22

Pb(NO3)2 (aq) + KI(aq) PbI2 (s) + KNO3(Aq)

Reactants

Pb- N-O-K-I-

Products

Pb- N-O-K-I-

12611

11312

C) Balancing Chemical Equations

The conservation of mass says that you must equal amounts of reactants and products

You can never change the chemical formulas in the equation*DO NOT CHANGE THE CHEMICAL FORMULAS*

You can only alter the equation to balance it by adding coefficients, big numbers in from of a chemical formula to make everything equal

___Pb(NO3)2 (aq) + ___KI(aq) ___PbI2 (s) + ____KNO3(Aq)

___Pb(NO3)2 (aq) + ___KI(aq) ___PbI2 (s) +____KNO3(Aq)

Reactants

Pb- N-O-K-I-

Products

Pb- N-O-K-I-

12611

11312

___Pb(NO3)2 (aq) + ___KI(aq) ___PbI2 (s) +____KNO3(Aq)

Reactants

Pb- N-O-K-I-

Products

Pb- N-O-K-I-

12622

11312

2

___Pb(NO3)2 (aq) + ___KI(aq) ___PbI2 (s) +____KNO3(Aq)

Reactants

Pb- N-O-K-I-

Products

Pb- N-O-K-I-

12622

12622

2 2

Pb(NO3)2 (aq) + 2KI(aq) PbI2 (s) + 2KNO3(Aq)

Practice Equations

SnO2 + H2 → Sn + H2O

C3H8(g) + O2(g) CO2(g)+ H2O(g)

N2 + H2 → NH3

Na(s) + HCl(aq) → NaCl(aq) + H2(g)

B4H10(g) + O2(g) -- B2O3(g) + H2O(g)

Na3PO4 + Fe2O3 -- Na2O + FePO4

NaCl(aq) + AgNO3(aq) → NaNO3(aq) + AgCl(s)